# -*- coding: utf-8 -*-
#
import numpy


def _z():
    return numpy.array([[0, 0]])


def _symm_r_0(r):
    return numpy.array([
        [+r, 0],
        [-r, 0],
        [0, +r],
        [0, -r],
        ])


def _symm_s(s):
    return numpy.array([
        [+s, +s],
        [-s, +s],
        [+s, -s],
        [-s, -s],
        ])


def _symm_s_t(s, t):
    return numpy.array([
        [+s, +t],
        [-s, +t],
        [+s, -t],
        [-s, -t],
        [+t, +s],
        [-t, +s],
        [+t, -s],
        [-t, -s],
        ])


def _pm(s, t):
    return numpy.array([
        [+s, +t],
        [-s, -t],
        ])


def _pm2(s, t):
    return numpy.array([
        [+s, +t],
        [-s, +t],
        [+s, -t],
        [-s, -t],
        ])
